In recent years, lifestyle-related diseases have become a problem. Among these, particular attention has been focused on metabolic syndrome. One of the causes of metabolic syndrome is the accumulation of visceral fat. In Japan, a number of diagnostic standards have been announced for metabolic syndrome.
In accordance with one of these standards, if a person has two or more of the symptoms listed below, there is a strong suspicion of metabolic syndrome:
Individuals with visceral fat-type obesity, specifically males with abdominal girth of 85 cm or more, and females with abdominal girth of 90 cm or more; and                Systolic blood pressure of 130 mmHg or more, or diastolic blood pressure of 85 mmHg or more,        Blood glucose of 100 mg/dL or more on an empty stomach, and        Blood neutral lipid value of 150 mg/dL or more, or HDL cholesterol of less than 40 mg/dL.In addition, cases corresponding to any one of the symptoms above are defined as belonging to the potential metabolic syndrome group.        
Previously, the method for treatment and amelioration of metabolic syndrome consisted mainly of food restrictions and exercise treatment. In addition, drugs for individual treatment of the above symptoms have been used as drugs for treatment and amelioration of metabolic syndrome. For example, diabetic treatment drugs, antihypertensive drugs, and antihyperlipidemia drugs, as well as other drugs that lessen white adipose tissue, blood glucose values, blood insulin concentrations, blood cholesterol, blood LDL cholesterol, and blood free fatty acid concentrations, have been used for treatment and amelioration of metabolic syndrome.
In such a circumstance, the development of new ameliorating agents and foods that are effective against the symptoms of metabolic syndrome is strongly desired. In particular, attention is being focused on the efficacy of food and other naturally derived constituents, and an ameliorating agent derived from natural substances is desired.
Fish oil is known to have various effects on the body. Research on efficacy on the body has been performed on some of Omega-3 polyunsaturated fatty acids (n-3 PUFAs). In particular, eicosapentaenoic acid (hereafter called “EPA”) and docosahexaenoic acid (hereafter called “DHA”) in fish oil are reported to have such effects as prevention of arteriosclerosis, prevention of heart disease, reduction of neutral lipids, prevention of hypertension, amelioration of diabetes, etc.
For example, in Non-patent Document 1, it was reported that n-3 PUFAs such as EPA and DHA improve lipid metabolism, and suppress increases in body weight.
In addition, in Non-patent Document 2, it was reported that n-3 PUFAs such as EPA and DHA induce the expression of adiponectin in adipose cells, to boost the plasma adiponectin levels.
In regard to fatty acid composition, it is known that the characteristic fatty acid composition in fish oil will vary depending on the type of fish. For example, saury, Alaska pollock, capelin, herring, and other offshore swimming fish are, in addition to long-chain n-3 PUFAs, also rich in long-chain monounsaturated fatty acids (MUFAs).
In regard to long-chain MUFAs, it was disclosed in animal experiments and human trials that monoenoic acids having 20 carbons and monoenoic acids having 22 carbons have a reducing action on blood glucose values (Patent Document 1). However, aside from the reducing action on blood glucose values, the physiological action of long-chain MUFAs has not been studied.
In addition, in regard to PUFAs and long-chain MUFAs, the physiological actions of these fatty acids are generally known to show different efficacy depending on the carbon number, as well as the number and positions of double bonds. Regarding the many fatty acids with differing carbon numbers, as well as the number and positions of double bonds, there are a large number of fatty acids remaining for which the physiological actions have not yet been studied. As a result, there is a possibility of further physiological actions existing for PUFAs and long-chain MUFAs, and the discovery of new physiological actions is desired.